1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof.
2. Description of the Related Art
As a conventional technology serving as a background of the present invention, there is a semiconductor device described in Japanese Patent Laid-Open Publication No. H6-342915 “MOS Type Power Semiconductor Device Including Protection Element and Manufacturing Method Thereof” shown in Patent Document 1. The semiconductor device described in Patent Document 1 includes not only a mechanism for discharging static electricity applied to an external gate electrode terminal exposed to the outside but also a resistor having a large sheet resistance, which is for use in protecting a gate electrode from the static electricity, in a gate electrode terminal, thus making it possible to effectively prevent a breakage of a gate insulating film owing to the static electricity.
Specifically, in Patent Document 1, when an object charged with the static electricity, such as a human body, is brought into contact with the external gate electrode terminal of the semiconductor device, the static electricity is discharged from the external gate electrode terminal to a source electrode at a ground potential through a bidirectional Zener diode provided as the mechanism for discharging the static electricity, that is, as such an electrostatic discharge protection element while bypassing the gate electrode. Meanwhile, a part of the static electricity applied to the external gate electrode terminal enters the gate electrode through the resistor for the protection from the static electricity, and is then diffused into the inside of the gate electrode. However, in the conventional technology described in Patent Document 1, a sheet resistance of a semiconductor thin film that forms the resistor is made larger than a sheet resistance of a semiconductor thin film that forms the gate electrode. In such a way, the static electricity that has entered the gate electrode is diffused rapidly into the gate electrode to reduce a density of the static electricity, a high electric field is prevented from being applied to the gate insulating film, and the breakage of the gate insulating film is prevented.